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Sprintosaur
the 'sprintosaurs '(Family Sprintosauridae) evolved from the duckbilled hadrosaurs of the late Cretaceous. In the last 65 million years, as the forests gradually gave way to the grasslands, the hadrosaurs evolved to adapt to the changing habitats. Like the hadrosaurs before them, there are two main groups of sprintosaur, the crested, and the non-crested. The crested sprintosaurs tend to inhabit the western high prairies, grazing the short grasses and undergrowth of prickly pear cactus in the dry shadow of the mountains. In the long evenings of the mating season the thin upland air resonates to the shrill trumpeting sounds as the sprintosaurs call to one another, using the hollow crests as sounding tubes. The crests are formed from the bones of the nose. They probably evolved to extend the nasal passage and allow dry air to pass over moist membranes before reaching the lungs. They successfully perform this function, because the air of the high prairie is very dry. Distinctively shaped crests are found in different species of crested sprintosaur and serve to distinguish members of one species from another, as they roam the sparse grasslands below the mountain ramparts. Both male and female sprintosaurs possess the crest. The non-crested sprintosaurs, like their slightly larger crested cousins, evolved from the hadrosaurs. However, while the crested forms evolved from such crested hadrosaurs as Corythosaurus and Parasaurolophus, the non-crested forms evolved from the flat-headed line of the hadrosaur group that included Hadrosaurus and Anatosaurus. Since Cretaceous times, their evolution into a grassland animal was parallel to that of the crested sprintosaurs. The cropping beak and the huge battery of constantly replaced grinding teeth needed little modification to suit a diet of tough, silica-rich grasses. As their faces were permanently in the grass, eating, the animal adopted a four-footed posture. On the open plains danger can be seen from a long way off and so the legs became spindly and lightweight to enable the animal to run swiftly from harm. The face became long to keep the eyes above the level of the grass so that a lookout could be kept for predators while grazing. The main difference between the non-crested and crested sprintosaurs, apart from the crest, is the presence of the tail. Having lost its function as a counterbalance, necessary when its ancestors went about on two legs, the tail has become a tall, stiff flagpost. The males have a fin of skin supported by bony struts at the tip, and this is used for signalling. Different species have different sizes and patterns of fin. The non-crested sprintosaurs live mainly on the long-grass, lowland prairie where the adaptations of the particularly long face and the tail flag are of most use. The sprintosaurs, both crested and non-crested types, travel over the plains in closely knit herds. The sprintosaurs evolved from the duckbilled dinosaurs of the Cretaceous period. These, in turn, evolved from completely bipedal dinosaurs but began to spend more time on all four legs. When they evolved into the plains-living sprintosaurs, they became completely quadrupedal. The legs are long and lightweight, with muscles concentrated in the thighs and upper arms, and the tail, having lost its balancing function, has degenerated either to a stump or to a flagpole. Crests vary from species to species and are used as signalling and identification devices. The shapes range from hook shapes, as in Ancorachephalus major, through rows of knobs, as in Sprintosaurus quadribullus, to broad blade shapes, as in S. dolabratops.